Wafer support table

Abstract

A wafer support table includes a ceramic base and a rod. The ceramic base has a wafer placement surface and includes an RF electrode and a heater electrode that are embedded therein in the mentioned order from the side closer to the wafer placement surface. A hole is formed in the ceramic base to extend from a rear surface toward the RF electrode. The rod is made of Ni or Kovar, is bonded to a tablet exposed at a bottom surface of the hole, and supplies radio-frequency electric power to the RF electrode therethrough. An Au thin film is coated over a region of an outer peripheral surface of the rod ranging from a base end of the rod to a predetermined position.

What is claimed is: 
     
       1. A wafer support table comprising:
 a ceramic base having a wafer placement surface and including an RF electrode and a heater electrode that are embedded in the ceramic base in mentioned order from side closer to the wafer placement surface; 
 a hole formed in the ceramic base to extend, toward the RF electrode, from a surface of the ceramic base on side opposite to the wafer placement surface; 
 a Ni- or an alloy of Fe, Ni, and Co-made rod bonded to the RF electrode exposed at a bottom surface of the hole or to a conductive member that is connected to the RF electrode and exposed at the bottom surface of the hole, and supplying radio-frequency electric power to the RF electrode therethrough; and 
 a thin film of a copper family element coated over a region of an outer peripheral surface of the rod ranging from a base end of the rod to a predetermined position at which the rod is not inserted in the hole, 
 wherein the thin film of the copper family element is formed not to cover a region of the outer peripheral surface of the rod positioned inside the ceramic base, and to cover less than the entire other region of the outer peripheral surface of the rod, which is not positioned inside the ceramic base. 
 
     
     
       2. The wafer support table according to  claim 1 , wherein the thin film of the copper family element has a thickness of not less than 3 μm and not more than 6 μm. 
     
     
       3. The wafer support table according to  claim 1 , wherein the predetermined position is determined by bonding a bare rod not coated with the thin film of the copper family element instead of the rod coated with the thin film of the copper family element, a temperature of the heater electrode is denoted by Ts, where Ts is higher than the Curie point of a material of the rod, a length of the rod is denoted by L [cm], a difference in temperature between both ends of the rod is denoted by ΔT [° C.], a length from a tip end of the rod to the predetermined position is denoted by x [cm], and a temperature at the predetermined position of the rod is denoted by T(x) [° C.], the predetermined position is determined such that T(x) expressed by a formula given below is not higher than the Curie point of the material of the rod;
     T ( x )= Ts −(Δ T/L )* x  
 
 
     
     
       4. The wafer support table according to  claim 2 , wherein the predetermined position is determined by bonding a bare rod not coated with the thin film of the copper family element instead of the rod coated with the thin film of the copper family element, a temperature of the heater electrode is denoted by Ts [° C.], where Ts is higher than the Curie point of a material of the rod, a length of the rod is denoted by L [cm], a difference in temperature between both ends of the rod is denoted by ΔT [° C.], a length from a tip end of the rod to the predetermined position is denoted by x [cm], and a temperature at the predetermined position of the rod is denoted by T(x) [° C.], the predetermined position is determined such that T(x) expressed by a formula given below is not higher than the Curie point of the material of the rod;
     T ( x )= Ts −(Δ T/L )* x  
 
 
     
     
       5. The wafer support table according to  claim 1 , wherein a thread groove is formed in an inner peripheral surface of the hole,
 a sleeve made of the same material as that of the rod and including a thread ridge formed on its outer peripheral surface is screwed into the hole and brazed, and 
 a tip end of the rod is inserted into the sleeve and is brazed to an inner peripheral surface of the sleeve.